1. Field of the Invention
The invention relates to a wheel axle and drive shaft or universal shaft for vehicle wheels with automatic pressure medium feed and discharge by way of the vehicle, where the pressure medium, air or other gases, during the motion of the vehicle is fed to the wheels by the vehicle itself, the tire pressure being regulated by the on-board computer.
2. Description of the Prior Art
Wrong tire pressure in the wheels results in heating and eventually in bursting of the tires. If the tire bursts at high velocity, increased risks of accidents arise. In addition, each of the tires, as a function of the road surface, load condition, ambient temperature, tire size, type of tire and weather conditions, requires a different tire pressure. In some countries the indication and control of the tire pressure condition has meanwhile become obligatory.
For more than 100 years, motor vehicles have been constructed with tires filled with compressed air. Efforts in this art to have the tire pressure regulated by the vehicle itself whilst in motion are known from numerous patent applications. In general, the solution attempts show two different principles. Whereas the first group of inventors endeavors to produce a permanent connection between the tire pressure and the compressed air on the vehicle side, the second group switches this connection on and off whenever required in order to reduce as much as possible the wear of valves and sealing means. In addition, in almost all of the solution attempts, it is endeavored to pass the air from fixed parts of the vehicle by way of radial passages into the revolving parts and to seal these passages on both sides by known radial sealing gaskets. This causes an increase in the number and the length of the sealing areas, and thereby also the friction and wear. It is important to note that attempts to date to solve this problem have not attained any breakthrough. All of them have failed to solve the problem completely, simply and in an adequately reliable manner, for which reason they have not to date attained production status and large scale production.
Thus, DE 697 04 067 T2 discloses a driven universal shaft, which, only when supplementation is needed, feeds the compressed air radially by way of a sealing unit specially designed for this purpose from one side only, i.e. only in the direction towards the non-return valve of the tire in the centre of the wheel rim. The revolving wheel hub itself has no valve. This system offers the advantage that, in the pressureless state, it is not subjected to friction or wear. It operates according to a principle similar to that of a disc brake which, in the absence of pressure, makes no contact with the revolving part. However, the disadvantages of this system are enormous. It has numerous, at least ten, complicated components. Initially, it allows much air to escape before the membrane couplings respond and cause sealing of the sealing surfaces. It requires maintaining predetermined geometrical conditions in order for the force onto the surface of the sealing elements to exceed the force which endeavors to lift the sealing elements and last but not least this system forwards the air to the tire only in one direction and requires very extensive assembly and dismantling work.
DE 40 29 311 C2 discloses a method for solving the set objective. In this method, the compressed air is forwarded by way of radial passages (19) of the revolving universal shaft and from there by way of oblique radial and axial bores (20) to a valve connected on one side to the universal shaft and on the other side to the pneumatically activated valve connected to the tire duct (40). This method has the advantage that it connects only when required, i.e. intermittently the tire air space to the source of air of the vehicle for regulating purposes. Operation of the operating valve (3) proceeds pneumatically by impulses by way of the existing compressed air and, accordingly, requires no additional ducting with slip rings to the revolving wheel hub (27). This method suffers from the following disadvantages: For sealing the air passage two static and two dynamic radial sealing rings (42) as well as additional mechanical components are required. The operating valve (3) is permanently connected to the wheel hub. The tire tube (40) is screwed under tire pressure to the operating valve. When changing wheels, e.g. from winter- to summer tires and vice versa, the tire tube (40) must be separated from the valve (3), whereby the tire is emptied. In addition, the externally positioned tube represents a hazard as well as an unbalance.
DE 36 19 603 A1 discloses a fixed wheel axle (5) including a pneumatically operated coupling unit (9, 11) integrated with and alongside the wheel axle and which, when required, connects to the valve body placed centrally on the wheel rim and supplies the tire by way of the externally positioned duct (14) with compressed air. The coupling (9, 11) is made of a sealing material such as rubber and is fitted on the wheel side to the piston rod, through which a bore passes, of a pneumatically operated cylinder-piston-unit which is connected downstream of a differential pressure valve (24). A stated advantage of this system is that, in normal vehicle operation, no contact and therefore also no wear takes place. Shortly prior to the start, i.e. while the vehicle is stationary, after the key has been inserted into the ignition, the piston rod (6) with its bore, is moved by the pneumatic pressure against the piston surface (19) in opposition to the force of the resetting spring (18) towards the tire valve (12, 13), making air-tight contact therewith and causing the tire to be filled with the same compressed air which caused the coupling of the piston rod to the tire valve. Disadvantages of this system include the fact that, firstly, it involves a stationary, i.e. non-driven wheel axle, for which reason the compressed air regulation is to take place prior to starting the vehicle, i.e. whilst stationary. Furthermore, nothing is said about the actual problem of the interaction of the coupling head (9, 11) with the valve body (12, 13). How much pressure is to be applied to the coupling at this locality for sealing to be achieved? This pressure, including the pressure required for overcoming the friction in the sealing rings of the piston rod (6) with sufficient pressure for overcoming the force of the resetting spring (18) must not be more than the minimum tire pressure. Otherwise it will not be possible to reduce or to regulate the tire pressure, because this takes place by way of a single air passage. Moreover, the axle must be drilled through sufficiently far to accommodate the axially movable piston rod (6) and cause it to enter into axially movable sealing engagement with the sealing elements (18). The aforesaid disadvantages of this system are so great that a reliable function cannot be assured. For that reason, this system as well has not been proven successful in practice.
EP 1 738 936 A1 discloses a combined unit comprising a roller bearing set, the hollow centre of which is used for feeding compressed air to the wheel and tire. The sheet metal cover (50) which closes the bearing unit is referred to as an element of compressed air feeding, without its sealing function against a valve and hose (A, B) connected thereto being in any way explained. This publication relates to a bearing unit and does not solve the object of inter-connection. For as long as roller bearings have existed, these have always had a hollow centre portion, which could be used for any other purpose. It is with great astonishment that here a bearing unit with a hollow centre portion has been patented. The question arises as to inventive level and effort!
PCT/SE 99/01574 (WO 00/15451 A1) discloses feeding compressed air to a tire by way of a ring (4.1) which is fitted on the outside to the end face of a wheel (1). What is disclosed here relates to a revolving wheel of a tractor, the large wheel hub (3) of which is stationary and offers much room for the passage therethrough and fixing of components (5). The revolving ring (4.1) comprises an axial groove, in which a stationary seal is accommodated which conducts the compressed air to the revolving part of the vehicle wheel from the stationary component (6), which is fitted by means of a clamp outside of the vehicle, to the wheel axle. The stationary ring (6) is centered by means of the roller bearing (4.9) in relation to the wheel (4.1, 4.2) and is held on the axle by the member (5.1). This principle is presumably suitable for slowly travelling vehicles such as tractors, even though it is very expensive. A considerable disadvantage resides, however, in the large number and the very large diameter of the components involved in solving the object and in the arrangement on the outside of the vehicle wheel. The large diameter of the seal and the stripper (4.11) as well as the large roller bearing (4.9) suffice to render this system very expensive. Moreover, this principle is completely unsuitable for road vehicles such as passenger motor vehicles, because non-revolving components must be fitted to the outside of the wheel, which present a hazard for people, quite apart from the fact that driven wheels possess no fixed portion to which the stationary ring (6) could be fitted.